AIGaAs/GaAs Pnp HBTs have the potential for high frequency performance approaching that of Npn HBTs. To achieve this performance, it is necessary to dope the base as heavily n-type as possible. This heavy base doping results in large degeneracy in the base, which reduces the heterobarrier to reverse injection of electrons from the base into the emitter. High Al content in the emitter is desirable to maintain good injection efficiency. Incorporating a gradient in the base doping can introduce fields to sweep injected holes across the neutral base region, which reduces base transport time. DC and RF characteristics of Pnp HBTs with 40% and 75% Al in the emitter will be presented. f of 17 GHz and 1max of 39 GHz has been achieved in 2 jim x I 1 .im HBTs fabricated using a self-aligned ohmic contact process. Further improvement in performance should be possible.

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